#include <stdio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

double f(double x)
{
    return 2 * x * x * x - 4 * x * x + 3 * x - 6;
}

int main()
{
    double y;
    while (scanf("%lf", &y) == 1)
    {
        double mid, left = -10000, right = 10000;

        //printf("(%.4lf, %.4lf)\n", f(left), f(right));

        if (y < f(left) || y > f(right))
        {
            printf("NULL\n");
            continue;
        }

        while (fabs(left - right) > 1e-6)
        {
            mid = (left + right) / 2;
            double ans = f(mid);
            if (ans == y)
                break;
            else if (ans > y)
                right = mid;
            else /* ans < y */
                left = mid;
        }
        printf("%.4lf\n", mid);
    }
    return 0;
}
